Elastic wave device and method for manufacturing the same

Abstract

An elastic wave device includes a supporting substrate, a high-acoustic-velocity film stacked on the supporting substrate and in which an acoustic velocity of a bulk wave propagating therein is higher than an acoustic velocity of an elastic wave propagating in a piezoelectric film, a low-acoustic-velocity film stacked on the high-acoustic-velocity film and in which an acoustic velocity of a bulk wave propagating therein is lower than an acoustic velocity of a bulk wave propagating in the piezoelectric film, the piezoelectric film is stacked on the low-acoustic-velocity film, and an IDT electrode stacked on a surface of the piezoelectric film.

What is claimed is: 
     
       1. An elastic wave device including a piezoelectric film, the elastic wave device comprising:
 a high-acoustic-velocity supporting substrate in which an acoustic velocity of a bulk wave propagating therein is higher than an acoustic velocity of an elastic wave propagating in the piezoelectric film; 
 a low-acoustic-velocity film stacked on the high-acoustic-velocity supporting substrate, in which an acoustic velocity of a bulk wave propagating therein is lower than an acoustic velocity of a bulk wave propagating in the piezoelectric film; 
 the piezoelectric film stacked on the low-acoustic-velocity film; and 
 an IDT electrode disposed on a surface of the piezoelectric film; wherein 
 a thickness of the low-acoustic-velocity film stacked on the high-acoustic-velocity supporting substrate and disposed under the piezoelectric film is in a range of about 0.1λ to about 0.5λ where λ is a wavelength of an elastic wave determined by an electrode period of the IDT electrode. 
 
     
     
       2. The elastic wave device according to  claim 1 , wherein a portion of energy of an elastic wave propagating in the piezoelectric film is distributed into the low-acoustic-velocity film and the high-acoustic-velocity supporting substrate. 
     
     
       3. An elastic wave device including a piezoelectric film, the elastic wave device comprising:
 a supporting substrate; 
 a high-acoustic-velocity film disposed on the supporting substrate, in which an acoustic velocity of a bulk wave propagating therein is higher than an acoustic velocity of an elastic wave propagating in the piezoelectric film; 
 a low-acoustic-velocity film stacked on the high-acoustic-velocity film, in which an acoustic velocity of a bulk wave propagating therein is lower than an acoustic velocity of a bulk wave propagating in the piezoelectric film; 
 the piezoelectric film stacked on the low-acoustic-velocity film; and 
 an IDT electrode disposed on a surface of the piezoelectric film; wherein 
 a thickness of the low-acoustic-velocity film stacked on the high-acoustic-velocity film and disposed under the piezoelectric film is in a range of about 0.1λ to about 0.5λ, where λ is a wavelength of an elastic wave determined by an electrode period of the IDT electrode. 
 
     
     
       4. The elastic wave device according to  claim 3 , wherein a portion of energy of an elastic wave propagating in the piezoelectric film is distributed into the low-acoustic-velocity film and the high-acoustic-velocity film. 
     
     
       5. The elastic wave device according to  claim 1 , wherein the low-acoustic-velocity film is composed of silicon oxide or a film containing as a major component silicon oxide. 
     
     
       6. The elastic wave device according to  claim 3 , wherein a thickness of the piezoelectric film is about 1.5λ or less, where λ is a wavelength of an elastic wave determined by an electrode period of the IDT electrode. 
     
     
       7. The elastic wave device according to of  claim 1 , wherein a thickness of the piezoelectric film is in a range of about 0.05λ to about 0.5λ, where λ is a wavelength of an elastic wave determined by an electrode period of the IDT electrode. 
     
     
       8. The elastic wave device according to  claim 1 , wherein the piezoelectric film is composed of single-crystal lithium tantalate with Euler angles (0±5°, θ, ψ), and the Euler angles (0±5°, θ, ψ) are located in any one of a plurality of regions R 1  shown in  FIG. 17 . 
     
     
       9. The elastic wave device according to  claim 8 , wherein the Euler angles (0±5°, θ, ψ) of the piezoelectric film are located in any one of a plurality of regions R 2  shown in  FIG. 18 . 
     
     
       10. The elastic wave device according to  claim 1 , wherein a coefficient of linear expansion of the supporting substrate is lower than that of the piezoelectric film. 
     
     
       11. The elastic wave device according to  claim 1 , wherein a specific acoustic impedance of the low-acoustic-velocity film is lower than that of the piezoelectric film. 
     
     
       12. The elastic wave device according to  claim 1 , wherein a dielectric film is disposed on the piezoelectric film and the IDT electrode, and a surface acoustic wave propagates in the piezoelectric film. 
     
     
       13. The elastic wave device according to  claim 1 , wherein a dielectric film is disposed on the piezoelectric film and the IDT electrode, and a boundary acoustic wave propagates along a boundary between the piezoelectric film and the dielectric film. 
     
     
       14. The elastic wave device according to  claim 3 , wherein at least one of an adhesion layer, an underlying film, a low-acoustic-velocity layer, and a high-acoustic-velocity layer is disposed in at least one of boundaries between the piezoelectric film, the low-acoustic-velocity film, the high-acoustic-velocity film, and the supporting substrate. 
     
     
       15. The elastic wave device according to  claim 3 , wherein the low-acoustic-velocity film is composed of silicon oxide or a film containing as a major component silicon oxide. 
     
     
       16. The elastic wave device according to of  claim 3 , wherein a thickness of the piezoelectric film is in a range of about 0.05λ to about 0.5λ, where λ is a wavelength of an elastic wave determined by an electrode period of the IDT electrode. 
     
     
       17. The elastic wave device according to  claim 3 , wherein the piezoelectric film is composed of single-crystal lithium tantalate with Euler angles (0±5°, θ, ψ), and the Euler angles (0±5°, θ, ψ) are located in any one of a plurality of regions R 1  shown in  FIG. 17 . 
     
     
       18. The elastic wave device according to  claim 17 , wherein the Euler angles (0±5°, θ, ψ) of the piezoelectric film are located in any one of a plurality of regions R 2  shown in  FIG. 18 . 
     
     
       19. The elastic wave device according to  claim 3 , wherein a coefficient of linear expansion of the supporting substrate is lower than that of the piezoelectric film. 
     
     
       20. The elastic wave device according to  claim 3 , wherein a specific acoustic impedance of the low-acoustic-velocity film is lower than that of the piezoelectric film. 
     
     
       21. The elastic wave device according to  claim 3 , wherein a dielectric film is disposed on the piezoelectric film and the IDT electrode, and a surface acoustic wave propagates in the piezoelectric film. 
     
     
       22. The elastic wave device according to  claim 3 , wherein a dielectric film is disposed on the piezoelectric film and the IDT electrode, and a boundary acoustic wave propagates along a boundary between the piezoelectric film and the dielectric film. 
     
     
       23. The elastic wave device according to  claim 1 , wherein a direction of the thickness of the low-acoustic-velocity film is perpendicular to a propagation direction of acoustic waves in a cross-sectional view. 
     
     
       24. The elastic wave device according to  claim 3 , wherein a direction of the thickness of the low-acoustic-velocity film is perpendicular to a propagation direction of acoustic waves in a cross-sectional view. 
     
     
       25. An elastic wave device including a piezoelectric film, the elastic wave device comprising:
 a high-acoustic-velocity supporting substrate which includes at least one among aluminum nitride, aluminum oxide, silicon carbide, silicon nitride, silicon oxynitride, a DLC film, and diamond; 
 a low-acoustic-velocity film stacked on the high-acoustic-velocity supporting substrate which includes at least one among silicon oxide, glass, silicon oxynitride, tantalum oxide, and any material obtained by adding fluorine, carbon, or boron to silicon oxide; 
 the piezoelectric film stacked on the low-acoustic-velocity film which includes at least one among LiTaO 3 , LiNbO 3 , ZnO, AlN and PZT; and 
 an IDT electrode disposed on a surface of the piezoelectric film; wherein 
 a thickness of the low-acoustic-velocity film stacked on the high-acoustic-velocity supporting substrate and disposed under the piezoelectric film is in a range of about 0.1λ to about 0.5λ; and 
 where λ is a wavelength of an elastic wave determined by an electrode period of the IDT electrode. 
 
     
     
       26. An elastic wave device including a piezoelectric film, the elastic wave device comprising:
 a supporting substrate; 
 a high-acoustic-velocity film disposed on the supporting substrate which includes at least one among aluminum nitride, aluminum oxide, silicon carbide, silicon nitride, silicon oxynitride, a DLC film, and diamond; 
 a low-acoustic-velocity film stacked on the high-acoustic-velocity film which includes at least one among silicon oxide, glass, silicon oxynitride, tantalum oxide, and any material obtained by adding fluorine, carbon, or boron to silicon oxide; 
 the piezoelectric film stacked on the low-acoustic-velocity film which includes at least one among LiTaO 3 , LiNbO 3 , ZnO, AlN and PZT; and 
 an IDT electrode disposed on a surface of the piezoelectric film; wherein 
 a thickness of the low-acoustic-velocity film stacked on the high-acoustic-velocity film and disposed under the piezoelectric film is in a range of about 0.1λ to about 0.5λ; and 
 where λ is a wavelength of an elastic wave determined by an electrode period of the IDT electrode.